This invention relates to a terahertz antenna and to a method for producing a terahertz antenna. Known terahertz antennas have at least one photoconductive semiconductor layer which is electrically contacted with antenna elements (e.g. antenna wings) for frequencies in the terahertz range (i.e. for frequencies in the range of 0.1-10 THz). Between the antenna elements, the photoconductive semiconductor layer of such terahertz antennas is illuminated with modulated light, in particular in the form of optical pulses (e.g. with a pulse length in the range of 100 fs) or a radiation modulated at high frequency. The irradiated light generates free charge carriers in the photoconductor, wherein by applying a voltage to the antenna elements the generated modulated charge carriers are accelerated. The accelerated charge carriers generate electromagnetic radiation with the modulation frequency, i.e. the terahertz antenna is operated as a terahertz transmitter.
When the terahertz antenna is operated as a terahertz receiver, a terahertz wave impinging on the photoconductive semiconductor layer induces a voltage between the antenna elements. This voltage causes a photocurrent in the semiconductor when the modulated illumination of the photoconductive semiconductor layer is effected in synchronism with the induced voltage. By measuring a mean photocurrent in dependence on the relative phase position of the terahertz radiation and the illumination modulation, both the amplitude and the phase of the terahertz radiation can be detected (coherent detection).
The photoconductive layer must consist of a material which among other things provides for an ultrafast recombination of the generated charge carriers (e.g. with recombination times of less than one picosecond), so that the generated photocurrent can at least approximately follow the modulated illumination. Furthermore, the material of the photoconductive layer should have a mobility of the photocharge carriers as high as possible in order to provide for an acceleration of the charge carriers as efficient as possible. One possibility for achieving the shortest possible recombination times is the generation of impurity centers by doping the photoconductor material. According to U.S. Pat. No. 8,809,092 B2, for example, the photoconductive layer is grown by MOVPE, wherein during the epitaxy a doping material (iron) is incorporated. At higher dopant concentrations, however, iron clusters are obtained in this method, which impair the terahertz properties of the photoconductive layer.